Conventionally, an induction heating cooker of this type is configured to directly sense infrared radiation radiated from a cooking vessel placed on a top plate, and it is known for its excellent thermal responsiveness. For example, PATENT DOCUMENT 1 (Japanese Unexamined Patent Publication No. 2004-273303) discloses an induction heating cooker of this type.
PATENT DOCUMENT 1 discloses an induction heating cooker including: a magnetic field shielding member that suppresses magnetic flux leakage from a heating coil disposed below a top plate; an infrared sensor that senses infrared radiation radiated from a cooking vessel placed on the top plate; and a control circuit that controls an output of the heating coil based on a sensing signal from the infrared sensor. In the induction heating cooker disclosed in PATENT DOCUMENT 1, in order to suppress the infrared sensor from generating heat due to a magnetic field generated by the heating coil, the infrared sensor is disposed at a position lower than the magnetic field shielding member.
Further, FIG. 8 shows the structure of another conventional induction heating cooker other than that disclosed in PATENT DOCUMENT 1. As shown in FIG. 8, the conventional induction heating cooker has a box-like shape whose top portion is open, and includes a body 1 which structures an outer casing of the cooker. At the top portion of the body 1, a flat top plate 3 on which a cooking vessel 2 is placed is provided so as to cover the top opening of the body 1.
In the body 1 and below the top plate 3, a heating coil 4 that inductively heats the cooking vessel 2 is placed. Below the heating coil 4, a plurality of ferrite elements 5 possessing magnetic field attraction are radially placed. The ferrite elements 5 suppress the magnetic field generated by the heating coil 4 from proceeding further below the ferrite elements 5.
At a position below the top plate 3 and facing to the cooking vessel 2, an infrared sensor 6 is placed. The infrared sensor 6 senses infrared radiation having radiated from the bottom surface of the cooking vessel 2 and passed through the top plate 3. Below the infrared sensor 6, a control circuit 7 that controls the output of the heating coil 4 based on the output signal from the infrared sensor 6 is placed.
The control circuit 7 is disposed in a cooling air path 11 formed between a partition plate 10 placed below the heating coil 4 and the bottom portion of the body 1. In the control circuit 7, a heat generating component 8 such as an insulated gate bipolar transistor (hereinafter referred to as an IGBT) joined to a heatsink or a resonance capacitor is installed. Further, inside the body 1, an air blower 9 that sends cooling air to the cooling air path 11 is provided. By the air blower 9 sending the cooling air, the heat generating component 8 is cooled to a desired temperature.
The heating coil 4 is attached to the top surface of a coil base 13 that stores therein the ferrite elements 5 by an adhesive or the like. The coil base 13 is supported by springs 12 placed on the partition plate 10, so as to be pressed against the bottom surface of the top plate 4 having the spacer 16 interposed therebetween. The spacer 16 is disposed between the coil base 13 and the top plate 4 for forming space between the heating coil 4 and the top plate 3.
The infrared sensor 6 is disposed below the ferrite elements 5 and above the partition plate 10. The infrared sensor 6 is disposed in a magnetic field shielding case 14 formed with aluminum or the like that exhibits the magnetic field shielding effect. Thus, the infrared sensor 6 is less affected by the magnetic field generated from the heating coil 4, thanks to the magnetic field shielding effect of the ferrite elements 5 and the magnetic field shielding case 14.
Further, the magnetic field shielding case 14 is affected by heat generated from the heating coil 4 or the cooking vessel 2 while cooking is carried out. Thus, the temperature inside the magnetic field shielding case 14, that is, the ambient temperature around the infrared sensor 6 rises. When the ambient temperature of the infrared sensor 6 becomes high, the output signal of the infrared sensor 6 varies as being affected by the ambient temperature, and the temperature sensing precision of the infrared sensor 6 is impaired. Therefore, the partition plate 10 is provided with an airflow vent 15 near the infrared sensor 6. Through the airflow vent 15, part of the cooling air from the air blower 9 blows in the magnetic field shielding case 14, whereby the magnetic field shielding case 14 is cooled, and the ambient temperature of the infrared sensor 6 drops. Thus, a reduction in the temperature sensing precision of the infrared sensor 6 is suppressed.    PATENT DOCUMENT 1: Japanese Unexamined Patent Publication No. 2004-273303